Traditionally, a flexible cover can be used to cover a cargo bed of a pick-up truck for protecting the cargos stored in the cargo bed. The flexible cover can be made of fabric, flexible plastic, or other sheet material, such as canvas, vinyl plastic or a weather-resistant fabric. The flexible cover is commonly secured to a metal frame on the edge of the cargo bed by means of reversible attachment. Because the pick-up truck generally are used and stored outdoors, the fabric cover and the reversible attachment means to the metal frame are exposed to the moisture, extreme heat and cold, dust, mud, rocks and other external material transported in the cargo bed. The exposure to the external material causes problems for the covering and the structure used to reversibly attach the flexible cover to the metal frame.
For solving the foregoing problem, please refer now to FIGS. 1, 2 and 3, U.S. Pat. No. 6,575,520 discloses a traditional flexible tonneau cover system of a pick-up truck, which uses an automatically adjustable hook and loop fastening design, wherein the flexible tonneau cover system is installed on a cargo bed 11 of a pick-up truck 10, and the flexible tonneau cover system comprises a pair of side rails 20, a flexible cover assembly 30, a rear header guide 40, a plurality of clamps 50, two hook and loop fastening systems 60 and a tension control assembly 70. The two side rails 20 are mounted on the top of two side walls 12 of the cargo bed 11 by the clamps 50; the flexible cover assembly 30 is mounted above a front wall 13 of the cargo bed 11; and the rear header guide 40 is mounted on the rear end of the two side rails 20 close to a tailgate 14 of the pick-up truck 10. The flexible cover assembly 30 has a front header 31, a flexible cover material 32 and a rear header (not-shown), wherein two ends of the front header 31 is installed on the front end of the two side rails 20; the flexible cover material 32 can be rolled up on the front header 31 or be unrolled rearward on the two side rails 20 to cover the cargo bed 11; and the rear header can be engaged with or separated from the rear header guide 40. Each of the two hook and loop fastening systems 60 has a first fastener 61 and a second fastener 62. The first fastener 61 is attached to an elongated slat 63 by adhesives, chemical bonding, thermal fusion, or the like, wherein the elongated slat 63 is slidably inserted in a channel portion 21 of the side rail 20. Meanwhile, the second fastener 62 is attached to the flexible cover material 32 by stitching, adhesives, chemical bonding, fusion, and the like.
When the flexible cover material 32 is unrolled rearward on the two side rails 20 to cover the cargo bed 11, the first fastener 61 and the second fastener 62 can be engaged with each other to provide a weatherproof seal without gaps that will protect the cargos in the cargo bed 11 from rain, wind, and blowing debris. At the same time, the tension control assembly 70 is used to automatically control the tension of the flexible cover material 32 by virtue of the inherent operation of spring plunger therein or manually control the tension by adjustments of a user, wherein the front header 31 will shift either slightly forward or slightly back, so as to achieve the desired tension. The tension can be adjusted to accommodate expansion or contraction of the flexible cover material 32 in response to climactic conditions. When the flexible cover material 32 is slightly shifted forward or backward, the combination of the second fastener 62, the first fastener 61 and the elongated slat 63 is slid along the channel portion 21 of the side rail 20 for carrying out the corresponding position adjustment.
However, there are still problems existing in the actual use of the traditional flexible tonneau cover system, as follows: During rolling up the flexible cover material 32, the second fastener 62 must be separated from the first fastener 61 adhesively attached to the elongated slat 63, wherein the separation force will damage the adhesion strength between the first fastener 61 and the elongated slat 63. After long-term use, the separation force will cause the first fastener 61 to be peeled off from the elongated slat 63. As a result, the structure of first fastener 61 and the elongated slat 63 must be replaced by a new one, resulting in increasing the usage inconvenience and the maintenance cost.
Furthermore, an inner surface of the elongated slat 63 is entirely in contact with a bottom surface of the channel portion 21 of the side rail 20. Thus, the contact area between the inner surface of the elongated slat 63 and the bottom surface of the channel portion 21 is too large. Meanwhile, an upper end and a lower end of the elongated slat 63 are entirely in contact with and clamped by two curved surface 22 of the channel portion 21. Thus, the contact area between the upper and lower ends of the elongated slat 63 and the curved surface 22 of the channel portion 21 is also too large. As a result, when the elongated slat 63 wants to slide along the channel portion 21, the elongated slat 63 may be jammed due to the tight match relationship with the bottom surface and the curved surface 22 of the channel portion 21, resulting in affecting the reliability of automatically or manually controlling the tension of the flexible cover material 32.
As a result, it is necessary to provide a side fastening assembly for a flexible tonneau cover system of a pick-up truck to solve the problems existing in the conventional technologies, as described above.